Building block



FIG. 1 is a perspective view of a building block;

FIG. 2 is a front elevation thereof;

FIG. 3 is a rear elevation thereof;

FIG. 4 is a left side elevation thereof;

FIG. 5 is a right side elevation thereof;

FIG. 6 is a top plan view thereof;

FIG. 7 is a bottom view thereof; and,

FIG. 8 is a perspective 3-D view of identical building blocks stacked next to each other. 

The ornamental design for a building block, as shown and described. 